Maximum likelihood detection of asynchronous servo data employing interpolation

Abstract

A repeatable run-out (RRO) detector employs one or more digital interpolators to interpolate asynchronous sample values representing an RRO address mark (AM) and RRO data, an asynchronous maximum-likelihood (AML) detector to detect the RRO AM, and a RRO data decoder to decode the RRO data. The AML detector employs an AML algorithm, such as a Viterbi algorithm, to detect the series of peaks of the RRO AM based on detection of the entire sequence of observed peaks. AML detection selects one of either the asynchronous or interpolated sample sequences that are closest in distance to the ideal RRO AM sample sequence. Once the RRO AM is detected, the AML detector provides a RRO AM found signal as well as the selected one of the sample sequences having the best phase for detecting and decoding the RRO data.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The present invention relates to detection of data in a communications system, and, more particularly, to detection of servo repeatable run out (RRO) information from a channel.[0003]2. Description of the Related Art[0004]A read channel integrated circuit (IC) is a component of a modem hard disk drive, such as a hard disk drive found in many PCs. A read channel component converts and encodes data to enable the (e.g., magnetic) recording head(s) to write data to the disk and then read back the data accurately. The disks in a hard disk drive typically include many tracks containing encoded data, and each track comprises one or more of user, (or “read”) data sectors as well as “servo” data sectors embedded between the read sectors. The information of the servo sectors aids in positioning the magnetic recording head over a track on the disk so that the information stored in the read sectors may be retrieved accurately.[0005...

AI Technical Summary

Benefits of technology

[0020]The present invention relates to repeatable run out data detection employing one or more digital interpolators to interpolate asynchronous sample values representing an address mark (AM) and data, an asynchronous maximum-likelihood (AML) detector to detect the AM, and a data decoder to decode the data. The AML detector employs an AML algorithm, such as a Viterbi algorithm, to detect the series of peaks of the AM based on detection of the entire sequence of observed peaks. AML detection selects one of either the asynchronous or interpolated sample sequences that are closest in distance to the ideal AM sample sequence. Once the AM is detected, the AML detector provides an AM-found signal as well as the selected one of the sample sequences havi...

Problems solved by technology

An imperfect spindle might not allow the disk in the hard drive to spin properly at the disk's center.

If the disk is not rotating at the center, then the track rotating under the head will not follow a circular trajectory, and hence the head might not be able to read the servo information properly.

Even though the disk may spin properly in a different hard disk drive while reading the servo information, since the information was not written properly on a circular track, the head might not be able to read the servo information accurately.

However, for RRO detection, it is not desirable to write a preamble for format efficiency reasons.

Also, detection of the RRO address mark is prone to detection errors because the RRO detector may begin detection in the DC erase field without the proper sampling phase (i.e., there is no preamble to guide the timing loop).

The performance of these detectors degrades significantly when the samples are generated with timing errors.

Since the sampling phase is not known when reading the RRO data field, a Viterbi detector is more prone to making errors.

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